Abstract: A barrier grid, in the form of a detention window, as employed in jail cells, or the like, is described. It is characterized by security bars which comprise and outer tube and a central core member extending lengthwise thereof. The tubes of the bars are secured to the window's frame. The central core member comprises a structural rod, rotatably mounted on a structural portion of the window frame. Each core member also includes a plurality of ceramic tubular elements which serve to dull a saw where the outer tube has been cut through in an escape. The ceramic elements are encased within a plastic sheath which serves to preserve the structural integrity of the ceramic elements.